All-D-Enantiomers of β-Amyloid Exhibit Similar Biological Properties to All-L-β-Amyloids

Abstract

The amyloidogenic peptide ␤-amyloid has previously been shown to bind to neurons in the form of fibrillar clusters on the cell surface, which induces neurodegeneration and activates a program of cell death characteristic of apoptosis. To further investigate the mechanism of A␤ neurotoxicity, we synthesized the all-D-and all-Lstereoisomers of the neurotoxic truncated form of A␤ (A␤ [25][26][27][28][29][30][31][32][33][34][35] ) and the full-length peptide (A␤ 1-42 ) and compared their physical and biological properties. We report that the purified peptides exhibit nearly identical structural and assembly characteristics as assessed by high performance liquid chromatography, electron microscopy, circular dichroism, and sedimentation analysis. In addition, both enantiomers induce similar levels of toxicity in cultured hippocampal neurons. These data suggest that the neurotoxic actions of A␤ result not from stereoisomer-specific ligand-receptor interactions but rather from A␤ cellular interactions in which fibril features of the amyloidogenic peptide are a critical feature. The promiscuous nature of these ␤-sheet-containing fibrils suggests that the accumulation of amyloidogenic peptides in vivo as extracellular deposits represents a site of bioactive peptides with the ability to provide inappropriate signals to cells leading to cellular degeneration and disease.Alzheimer's disease (AD), 1 vascular dementia, and hereditary cerebral hemorrhage with the Dutch type are diseases that share an invariant pathological feature, the accumulation of an amyloidogenic peptide into insoluble fibrillar extracellular deposits. In all three cases, the major component of the extracellular debris is the ␤-amyloid peptide (A␤) that is derived from the proteolytic processing of the large membraneanchored amyloid precursor protein (APP) encoded by a single gene located on chromosome 21 (1). However, the biological significance of these amyloid deposits has been extensively debated as to whether they are a causative factor of each disease or merely a metabolically inert end product lacking in biological activity. Evidence in support of a causative role for A␤ in neuropathology comes from genetic analysis of the APP gene where several autosomal dominant mutations have been linked with AD and hereditary cerebral hemorrhage with the Dutch type (2, 3). In a recent in vitro study, the ␤-APP 717 mutation consistently caused a significant increase in the percentage of the longer and more amyloidogenic A␤ 1-42 over the shorter A␤ 1-40 (4). Incorporation of this same mutation into a transgenic mouse model yields A␤ deposition and neuropathology that closely parallels that observed in AD (5). Additional in vivo evidence suggesting that the A␤ peptide itself may be biologically active comes from a transgenic model overexpressing A␤ , in which A␤ transgene expression was detected in a variety of peripheral tissues but histopathological changes were restricted to the brain. Moreover, the neurodegeneration was largely limited to the cerebral cortex, ...

Acceleration of Amyloid Fibril Formation by Specific Binding of Aβ-(1–40) Peptide to Ganglioside-containing Membrane Vesicles

“…We suggest an important significance of this finding because a correlation appears to exist between biological effects of A␤ and its aggregation state (7)(8)(9)(10). Furthermore, it is believed that the fibrillar peptide itself represents the neurotoxic species.…”

The Role of G Protein Activation in the Toxicity of Amyloidogenic Aβ-(1–40), Aβ-(25–35), and Bovine Calcitonin

“…Additionally, both the L-and D-enantiomers of A␤ exhibited nearly identical structural characteristics and induced similar levels of toxicity, implying that A␤ neurotoxicity was mediated by A␤ fibril features instead of any stereoisomer-specific interactions (79). Compounds such as Congo Red, rifampicin, and recognition peptides that bind to and/or inhibit the formation of amyloid fibrils have also been shown to attenuate the toxicity of A␤, further establishing the causal link between A␤ structure and function (21-24, 64, 80, 81).…”

Calcium Signaling and Amyloid Toxicity in Alzheimer Disease

“…Disruption of Membrane Lipid Integrity-A␤ peptides interact with membrane lipids such as phosphoinositides (51), phosphatidylglycerol (52), phosphatidylcholine (53), and gangliosides (54). A direct interaction of A␤ with cell membranes was initially proposed by Cotman and co-workers (55), who showed that D-and L-stereoisomers of a truncated form of A␤ induced similar toxicity levels in cultured hippocampal neurons, suggesting that A␤ toxicity does not involve a specific ligand-receptor interaction. Fluorescence spectroscopy measurements indicate that A␤ interaction with the synaptic plasma membrane causes substantial changes in the membrane fluidity both in the bulk lipid milieu and in proximity to integral membrane proteins.…”